A maple syrup extract alleviates liver injury in type 2 diabetic model mice

A recent study showed that 54% of type 2 diabetes (T2D) patients have nonalcoholic fatty liver disease, which is a risk factor for aggravation diabetic symptoms. Previous studies suggested components in maple syrup alleviated liver injury and found polyphenols as food components to improve the symptoms and complications of diabetes. Therefore, we hypothesized that a polyphenol fraction in maple syrup improves the symptoms and complications of diabetes. To address the hypothesis, we investigated the effects of a polyphenol-rich maple syrup extract (MSE) on a T2D model mice. KK-Ay mice were fed a normal or 0.1% MSE-supplemented diet for 43 days. The results showed that the levels of serum alanine aminotransferase and aspartate aminotransferase were significantly reduced in mice that ingested MSE. Hepatic genes related to lipogenesis and lipolysis were down- and upregulated, respectively, in mice that ingested MSE. These results suggest that MSE intake alleviates liver injury and suppresses lipid accumulation in the livers of T2D mice. Male KK-Ay mice 4 weeks of age were purchased from CLEA Japan (Tokyo, Japan). The mice were individually housed in a room maintained at 21–23°C with 50–70% relative humidity and a 12:12-h light/dark cycle. Normal and 0.1% MSE-supplemented diets were prepared based on the AIN-93G formula by Oriental Yeast Co. (Tokyo, Japan). The supplemented dose of MSE was decided on the basis of polyphenol content in our previous study. In the study, we showed that a liver injury marker decreased in healthy rat fed maple syrup-supplemented diet which had almost the same amount of polyphenol as the diet in this study. After one week of acclimation, the mice were divided into two groups (n = 8 each) with approximately equal mean body weights and nonfasting blood glucose levels. The mice were fed normal or MSE diets (the control or MSE group) with a pair-feeding technique for 43 days and allowed free access to ultrapure water. The food intake and body weight were measured every two and four days, respectively. After 16 h of food deprivation, the mice were sacrificed under sodium pentobarbital anesthesia. The liver was treated with RNAlater (Thermo Fisher Scientific Inc., Waltham, MA, USA). The samples were stored at −80°C until use.